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A101587 Indices of primes in sequence defined by A(0) = 51, A(n) = 10*A(n-1) + 71 for n > 0. 1
2, 4, 5, 20, 308, 815, 857, 1114, 1418, 1688, 12008, 18692, 28097, 90964 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that (530*10^n - 71)/9 is prime.

Numbers n such that digit 5 followed by n >= 0 occurrences of digit 8 followed by digit 1 is prime.

Numbers corresponding to terms <= 857 are certified primes.

a(15) > 10^5. - Robert Price, Sep 08 2015

REFERENCES

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

LINKS

Table of n, a(n) for n=1..14.

Makoto Kamada, Prime numbers of the form 588...881.

Index entries for primes involving repunits.

FORMULA

a(n) = A103022(n) - 1.

EXAMPLE

5881 is prime, hence 2 is a term.

MATHEMATICA

Select[Range[0, 300], PrimeQ[(530*10^# - 71)/9] &] (* Robert Price, Sep 08 2015 *)

PROG

(PARI) a=51; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a+71)

(PARI) for(n=0, 1500, if(isprime((530*10^n-71)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A103022.

Sequence in context: A101843 A192117 A084592 * A277853 A200906 A036986

Adjacent sequences:  A101584 A101585 A101586 * A101588 A101589 A101590

KEYWORD

nonn,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 09 2004

EXTENSIONS

1688 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008

a(11)-a(13) from Kamada data by Ray Chandler, Apr 30 2015

a(14) from Robert Price, Sep 08 2015

STATUS

approved

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Last modified November 16 17:04 EST 2019. Contains 329201 sequences. (Running on oeis4.)